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The tubes terminate inside an airless 16-ft.-wide aluminum chamber, each entering it from a different direction. Inside, the focusing lenses are arrayed around a pellet of deuterium and tritium, two heavier varieties of hydrogen atoms. Scientists hope that when the beams simultaneously hit the pellet, which is smaller than a grain of sand, the temperature of the pellet's outer surface will be raised to 100 million degrees, causing it to vaporize explosively. Just as a rocket is pushed forward by its tail exhaust, the vaporizing surface would exert a force inward, compressing the pellet to a density 20 times that of lead and forcing the nuclei to fuse. In the fusion power plant of the future, Livermore scientists say, larger pellets will be blasted, one after another, producing successive bursts of energy.
Critics of the laser fusion program contend that it is five to ten years behind magnetic containment fusion, a technique that uses powerful magnetic fields to contain the reaction. But magnetic fusion, too, still has a long way to go. It has not yet even reached the stage at which the energy produced by the machines equals the energy required to run them. Says Livermore's Emmett: "Fusion is one of the most difficult technological undertakings that man has ever engaged in, and probably one of the most important."